Net shaped dies and molds and method for producing the same

ABSTRACT

A method for making dies or molds from powdered metals is disclosed. The method includes the steps of: providing a pattern of a desired shape to define the mold or die cavity configuration; providing a canister; placing the pattern in the canister and filling the canister with a selected powdered metal; hot isostatic pressing the canister and powdered metal to produce a consolidated and densified compact; and sectioning the compact along a plane to enable removal of the pattern and thus providing the desired die or mold cavity in the fully densified powdered metal die or mold set so formed.

This application is a 371 filed Apr. 15, 1997. This application claimbenefits of provisional application 60/015,979 filed Apr. 15, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to the production of dies and molds madedirectly from powdered metals. The dies, according to the invention, aremade by placing a specially formed pattern, having the shape of thedesired die cavity, into a canister and fixing it in an appropriatelocation inside of the canister. The spaces between the pattern and thecanister are then filled with a selected powdered metal, evacuated andsealed. Hot Isostatic Pressing (HIP) is then used to consolidate thepowdered metal to full density. Separation of the compact along anappropriate plane enables the pattern to be removed thereby revealingthe desired die cavity formed in the consolidated powdered metal.

Present techniques for the production of dies involve casting ingots ofthe die material which must be reduced in size by rolling and/orforging. These steps result in significant yield loss of the materialand create less than ideal mechanical properties due to the coarsenature of the microstructure. Following the rolling or forging, it isnecessary to machine the cavity into the die. This is a very timeconsuming and labor intensive process which results in substantialexpense and in additional wasted material.

SUMMARY OF THE INVENTION

The present invention is directed to a method of making dies and moldsfor subsequent use in the manufacture of shaped parts, such as by diecasting, injection molding and the like. The method includes the stepsof providing a pattern of a desired shape to define the finished mold ordie cavity configuration; placing the pattern in a canister; filling theinterior of the canister with a selected powdered metal to surround thepattern therein; hot isostatic pressing the canister and powdered metalby the application of heat and pressure to consolidate and densify thepowdered metal surrounding the pattern; and sectioning the canister anddensified metal along a plane to remove the pattern and thus provide adie or mold cavity of desired shape in the densified metal sections.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross section through the centerline of a canister showingthe pattern with the space between the pattern and the canister filledwith powder according to the present invention;

FIG. 2 is a view of the canister of FIG. 1 after hot isostatic pressingshowing the sectioning lines;

FIG. 3 is a view showing the die with the pattern of FIGS. 1 and 2removed; and

FIG. 4 is a perspective view of a compacted die, after separation,showing the pattern and parting plate used in the method of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method of practicing this invention as shown in FIG. 1 involves thecreation of a steel pattern 4 by classical machining techniques. Thispattern is the size and shape of the desired cavity to be produced inthe finished die. The pattern is affixed to the bottom of the canister 8by tack welds 9. A coating of yttrium oxide 5 is applied to the surfaceof the pattern 4. In a separate operation, the fill/evacuation tube 1,top 2 and central portion of the canister 10 are welded together. Thisassembly is then welded to the bottom segment 8 of the canister.

Powder of the desired die material is then introduced into the canistervia the opening 7 in the fill/evacuation tube 1. The powder 6 in thisexample is M4 tool steel and fills the space between the pattern and theinternal surfaces of the canister. The air is evacuated from thecanister through the fill/evacuation tube 1 which is then welded closed.The canister containing the pattern and the powder is then hot isostaticpressed at 2175° F. for five hours at a pressure of 15,000 PSI. Thisprocess consolidates the powder creating a solid compact around thepattern.

In order to remove the pattern, the consolidated canister is bandsaw cutas shown in FIG. 2. Upon removal of the pattern halves from the compact,the desired die cavity is revealed, see FIG. 3.

A presently preferred embodiment of the invention is shown in FIG. 4. Inthis embodiment, a parting plate 11 is placed between the halves of thepattern 12. The parting plate 11 may be, for example, 1/2 inch thickcarbon steel. The parting plate is either integral with the pattern 12or may be pinned or tack welded thereto. The pattern is made slightlyoversized on each side of the parting plate to accommodate the thicknessof the parting plate. The assembled pattern and parting plate are coatedwith a parting agent such as boron nitride and are then positionedinside the canister 13. Tack welding or mechanical fasteners are used toattach the pattern/parting plate to the inside of the canister. Thecanister is then welded closed, incorporating a fill tube. In thisexample, H13 powder is introduced into the canister through the filltube followed by evacuation and sealing of the canister. Hot isostaticpressing at 2175° for five hours at 15,000 PSI consolidates the powderinto a solid.

Removal of the pattern is accomplished by cutting or milling the edgesof the canister to expose the edges of the parting plate. The die halvesare then separated from the pattern and the parting plate. The patternassembly may then be used to produce additional dies or molds.

While the above description is the currently preferred approach, thereare numerous variations which would be apparent to those of ordinaryskill in the art. These include, but are not limited to, changing thepowdered material used for the die. Obviously, this selection would bedetermined by the properties required in the final die or mold. Typicalmaterials generally classified as tool steels, nickel alloys, cobaltalloys and copper alloys could be used. The consolidation parameterswould then be selected for the alloy being used.

Also, the technique used to manufacture the patterns may includeforging, casting or selected layer sintering. It is also possible to useparts which were previously produced from dies made by the presentinvention.

Presently, yttrium oxide has been applied to the pattern to act as arelease coating to prevent the powder from bonding to the pattern duringthe consolidation process. Other choices of release agents or diffusionbarriers could be equally effective. These may include aluminum oxide,zirconium oxide, silicon dioxide, magnesium oxide, titanium oxide,thorium oxide, titanium carbide, titanium nitride and boron nitride. Itwould also be possible to create the release layer on the pattern bythermally treating the pattern in an oxidizing or nitriding environment.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. The presentlypreferred embodiments described herein are meant to be illustrative onlyand not limiting as to the scope of the invention which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

What is claimed is:
 1. A method of making dies and molds comprising thesteps of:providing a pattern having a desired shape to define one of adie or mold cavity; providing a canister having a hollow interior;placing the pattern in the hollow interior of the canister; filling thecanister with a powdered metal to surround the pattern therein; hotisostatic pressing the canister to consolidate and densify the powderedmetal; and sectioning the consolidated and densified powdered metal topermit removal of the pattern whereby one of a die or mold cavity isprovided.
 2. The method of claim 1 including the steps of evacuating airfrom the canister after the filling step and sealing the canister, as bywelding, after said evacuating step and before said hot isostaticpressing step.
 3. The method of claim 1 including the step of providinga flat plate around said pattern prior to said placing step, said plateextending outwardly from the pattern to the canister whereby a partingline is created by said plate after said pressing step.
 4. The method ofclaim 1 including the step of coating the pattern with a release agentto prevent the metal powder from bonding to the pattern during the hotisostatic pressing step.
 5. The method of claim 4 wherein the releaseagent is one selected from the group consisting of yttrium oxide,aluminum oxide, zirconium oxide, silicon dioxide, magnesium oxide,titanium oxide, thorium oxide, titanium carbide, titanium nitride andboron nitride.
 6. The method of claim 4 wherein the release agent iscreated by thermally treating the pattern in one of an oxidizing ornitriding atmosphere.
 7. The method of claim 1 wherein the hot isostaticpressing step is carried out at a pressure of about 15,000 PSI and at atemperature of about 2175° F. for about five hours.
 8. The method ofclaim 1 wherein the powdered metal is a powdered metal used for diematerials comprising one selected from the group consisting of toolsteels, nickel alloys, cobalt alloys and copper alloys.
 9. A method ofmaking dies and molds comprising the steps of:providing a pattern of adesired shape to define one of a die or mold cavity; providing acanister having a hollow interior; placing the pattern in the hollowinterior of the canister and affixing the pattern to the canister;coating the pattern with a layer of yttrium oxide; filling the canisterwith a powdered M4 tool steel to fill the space between the pattern andthe internal surfaces of the canister; evacuating air from the canister;sealing the evacuated canister by welding; consolidating and densifyingthe M4 tool steel powder by hot isostatic pressing the canister andcontained powder at a pressure of 15,000 PSI and at a temperature of2175° F. for a time of five hours; and sectioning the consolidated anddensified powdered metal and removing the pattern therefrom to provideone of a die or mold cavity.
 10. The method of claim 9 including thestep of providing a flat plate around said pattern prior to said placingstep, said plate extending outwardly from the pattern to the canisterwhereby a parting line is created by said plate after said pressingstep.
 11. A die or mold comprising a die set made by hot isostaticpressing powdered metal and having a die cavity of a desiredconfiguration formed therein during said hot isostatic pressingoperation.
 12. The die or mold of claim 11 wherein the powdered metal isone selected from the group consisting of tool steel, nickel alloy,cobalt alloy and copper alloy.
 13. The die or mold of claim 11 whereinthe powdered metal is an M4 tool steel.